Stabilization of polyethylene for thermal processing with sulfides of dialkyl phenols



United States Patent STABHLEZATION' OEPOLYETHYLENE FOR THER- MAL PROCESSING WITH SULFIDES 0F DIAL- KYL PHENOLS.

SamuelSteingiser, Bridgeville, Pa, and Ival 0. Salyer, Dayton, Ohio, assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Continuation ofapplication. Ser. No. 388,689, Oct. 27, 1953. This. application June 25,1964, Ser. No. 378,068

20 Claims. (C'l.260-45.95)

This invention relates to polymers of ethylene. In preferred aspects the invention pertains to the stabilization' of polyethylene against oxidative cross-linking during thermal processing. In other aspects the invention pertains to a particular class of compounds effective in very low concentrations to give stability to polyethylene during thermal processing.

This application is a continuation of our copending application Serial No. 388,689 filed October 27, 1953, now abandoned.

The term polyethylene as employed-herein refers to the normally solid high molecular weight polymers of ethylene. Such polymers usually have a molecular weight of atleast 6,000 and preferably for the. practice of this invention have a molecular weight of 20,-000Qto 30,000 or above. They havea waxy feel. When examined by the X-ray diifraction technique these polyethylenes exhibit'the presenceof a crystalline phase. Polyethylene suitable forthe practice of the present invention can readily be made by subjecting monomeric material consisting of or comprising ethylene, containing, say, 50 to 200 parts per million oxygen, to polymerization at very high pressures, for example, 15,000 to 40,000 pounds per square inch. Various other methods offpreparing solid polyethylene, for instance, by employing peroxide or azo catalysts and water or organic liquid reaction media along with moderately high pressures, for example, 5,000 to 10,000pounds per square inch, are well-known-in the art. The invention is applicable to homopolymers of ethylene,- and normally solid polyethylene-type materials which are copolymers of ethyleneand one ormore ethylenically unsaturated comonomers employed in an amountusually not toexceed "15 Weightpercent-of the ethylene, for instance, styrene, vinyl chloride, vinyl acetate, vinylidene chlorofluoride, methyl methacrylate.

Polyethylene is subject to degradation by heat and light. When polyethylene is mechanically worked in the presence of air at the elevated-temperatures necessary for processing and fabrication, oxidative cross-linking occurs wherein the polymer becomes lower in how, higher in elastic memory, and lower in tensile elongation. In addition, the originally excellent high and low frequency electrical resistivity of the. polymer becomes progressively poorer. Furthermore, cross-linking occurs upon prolonged exposure of the polymer to ultraviolet radiation in the presence of air. Stabilization against thermal-degradation is of prime importance. In all applications the polymer must be able to withstand the thermal :processing required in fabrication; whereas stabilization against'photodegradation although desirable isnotusually essential. Materials which have been suggested or used for thermalstabilization of polyethylene in the past are unsatisfactory for one or more of the following reasons: They impart a dark color to the product; and-this is obviously undesirable where it is necessary to produce a wide variety of light pastel colors. Established stabilizers are so ineificient-as to require relatively high concentrations which'impair electrcal and physical proper- 3,170,893 Patented Feb. 23, 1965 ties and are alsouneconomical. Many of thest'abilizers are toxic and cannot-be used in food applications -of'the product. Some 'of 'the older thermal stabilizers aresdestabilizers for photo initiated degradation. We have found that adverse effectsoficonventionalthermalstabilizers are eliminatedwith the discovery of class of materials which are'so efiicient that very. minutequantities can be used tofprovide: the'desir ed: protection-.1

In accordance with thenpresent invention in preferred embodiments, ethylene polymers have incorporateditherein a very small quantity, at' least sufficient; to minimize the undesirable effects of-thermal :PIOCGSSlHgi'Of a sulfide of a monohydric dial'kyl phenol in whichia carbon atom of each of two nuclei'of 'suchp-henol are joined together by less than three sulfur atoms and. each of'wthe. alkyl groupscontain less than. sixcarborr atoms. and at least one alkyl group is a branchedchain alkylgroup; and Which is unsubstituted, except1forsulfur, in two ofthe positions ortho and para to the hydroxy group. Preferred' sulfides of dialkyl phenols aremonosulfideS and disulfides, particularly the former, of alkyl cresols conformingto the-limitations given in the preceding sentence. More broadly, the invention encompasses thems'e of sulfides, especially monoand disulfides, of alkyl cresols in general. The'invention in its broadest. aspects employs sulfides of dialk-yl phen-ols'in general. Suitable dialkyl phenol sulfides are. availablecommercially. It is preferred that neither alkyl group. containtmore than-12 carbon atoms. Preferably each alkyl group'containsdss than 6 carbonatoms and-at least one is branched-chained, of which. the tertiary alkyl groups are. most: commonly used, e.g., tort-butyl, tert-amyl.

While, for the salient convenience,"the discussion'in the present application is principally 'directed to: sulfides of dialkyl phenols wherein in asinglemolecule both? the dialkyl phenol residues are of the-same. structure, it will be appreciated: that sulfides wherein the. two dialkyl phenol residues have different structuresarealso contemplated although suchcornpounds are not as conveniently made. Sulfides of dialkyl phenols. are conveniently-obtained by the action of sulfur. monochloride (S 01 or sulfur dichloride'(SCI onsthe diallcyl aromatiohydroxy compound. When convenient or' desirable other methods of synthesis may be=used, and.it is totbe understood that thisinventionis not limited to any particular method of synthesis but pertains broadly to th use of thematerials described.- However, it may be. pointed. out'that since more than one position at which thersulfur may attach to. the ring is available, more than. a single reaction product may be formed, andi it is'withinxthepurview of thissinvention to. employ the composite reaction products aswell as :pure. individual compoundsi- For example, thymoland carvacrolcre act readily with sulfur-dichloride in an organic solvent-to produce crystalline solids M.P. (purified) 152-153 C. and. 171472. C., respectively, and minoramounts of. other material which remains in the organic solvent. If the solvent is evaporated off without separating the crystalline solid, a composite resinous reaction productremains which is effective in the practice of the invention; Similarly, 4-tertiary butyl meta cresolreacts with'sulfur dichloride in ether solution producing a crystalline solid melting at 157- 158 C. and an even larger proportion of resinous reaction product. Again, the composite reaction product as well as the pure crystalline compound, can be incorporated in polyethylene in the. practice of theinvention.

One suitable method: of" preparation" comprises adding a solution of-sulfur. monochloride or dichloride-in carbon tetrachloride or. other suitablesolvent to a rapidly stirred solution of the dialkyl phenol in the same solvent. The reactions are usually instantaneous and take place with little evolution of heat. The mixture is then cooled to precipitate out the crystalline material and filtered, or where the product is a liquid or where it is desired to isolate the composite reaction product, the solvent is simply removed by evaporation or other suitable means. For example, sulfur dichloride is reacted in this manner with 3,5-xylenol, 3,5-dimethyl-4-chlorophen'ol, 6-tertbutylmeta-cresol, dodecyl-meta-cresol, and the like.

By way of example but not limitation, the following specific compounds can be named as examples of those which are incorporated in small amount with polyethylene in the practice of the invention: di(1-hydroxy 3- methyl 6-isopropyl phenyl) monosulfide and disulfide, di(1-hydroxy 3-methyl G-tertiary butyl phenyl) monosulfide and disulfide, di(l-hydroxy Z-tertiary butyl S-methyl phenyl) monosulfide and disulfide, di(1-hydroxy 2-tertiary amyl S-methyl phenyl) monosulfide and disulfide, di(l-1ydroxy 2-methyl S-isopropyl phenyl) monosulfide and disulfide, di(1-hydroxy 2-methyl S-tertiary butyl phenyl) monosulfide and disulfide, di(ll-hydroxy Z-methyl S-tertiary amyl phenyl) monosulfide and disulfide, di(1- -hydroxy 3-methyl 4-isopropyl phenyl) monosulfide and 4-methyl phenyl) monosulfide and disulfide, di(1-hydroxy 3-isopropyl 4-methyl phenyl) monosulfide and disulfide, di(l-hydroxy 3,6-ditertiary butyl phenyl) monosulfide and disulfide, di(1-hydroxy 2,5-ditertiary butyl phenyl) monosulfide and disulfide, di(l-hydroxy 2-methyl 3-isopropyl phenyl) monosulfide and disulfide, di(l-hydroxy Z-methyl 3-tertiary butyl phenyl) monosulfide and disulfide, di(1-hydroxy 3,5-ditertiary butyl phenyl) monosulfide and disulfide, di(l-hydroxy 3-methyl S-isopropyl phenyl) monosulfide and disulfide, di(1-hydroxy 3-rnethyl S-tertiary butyl phenyl) monosulfide and disulfide, di(1- hydroxy S-methyl S-tertiary amyl phenyl) monosulfide and disulfide, di(l-hydroxy 3-methyl 4-secondary butyl phenyl) monosulfide and disulfide, di(l-hydroxy 3-methyl 4-isoamyl phenyl) monosulfide and disulfide. Further examples of suitable compounds which are in general however less efiicacious in the practice of the invention are: di(1,-hydroxy 3-methyl 6-n-octyl phenyl) monosulfide and disulfide, di(1-hydroxy 3-methyl 6-methyl phenyl) monosulfide and disulfide, di(1-hydroxy Z-methyl 4-tertiary butyl phenyl) monosulfide and disulfide, di(l-hydroxy 2-hexyl S-hexyl phenyl) monosulfide and disulfide, di(l-hydroxy 3-methyl 4-chloro S-tertiary amyl phenyl) monosulfide and disulfide. Dialkyl phenol sulfides can be used which contain hydrocarbon groups other than alkyl, e.g., benzyl, phenyl, or non-hydrocarbon groups, e.g., chloro, that do not interfere with the desired effect of the dialkyl phenol sulfides on the ethylene polymers. It will, of course, be understood that some differences will be found in the actions of -these dialkyl phenol sulfides and that the various ones are not necessarily the full equivalents of each other in the practice of the invention.

The following structural formula can be used to represent a preferred group of dialkyl phenol sulfides carbon atoms at least one alkyl group on each nucleus being a branched-chain alkyl group.

H O OH where R is an alkyl radical containing up to 12 carbon atoms and n is an integer less than 3, and more preferably where R is a branched-chain alkyl radical containing less than 6 carbon atoms.

The sulfur bridge is usually para to the hydroxyl group, but the invention is not limited thereto. The amount of dialkyl phenol sulfide to employ in the practice of the invention will of course be dependent to a considerable extent upon the particular dialkyl phenol sulfide employed and upon the treatment to which the polyethylene is to be subjected and the ultimate use of the polyethylene. It will also depend to a somewhat lesser extent upon the particular characteristics of the ethylene polymer, its molecular weight, degree of branching, content of impurities, whether homopolymer or copolymer, and the like. It is a feature of the invention however that ethylene polymers are protected against undesirable effects of thermal processing by incorporation of extremely small amounts of dialkyl phenol sulfides. Thus, in many instances where the thermal processing is to be effected at temperatures below 200 C. and for periods of time not to exceed one hour, 500 parts per million, i.e., 500 parts by weight dialkyl phenol sulfide per million parts by weight ethylene polymer, and even as low as 50 parts per million and less, are effective. As will be seen in the specific examples hereinbelow, even-much smaller quantities than these exhibit a protective effect where the processing time is short. Usually no more than 0.1 Weight percent is needed. Those skilled in the art, having had the benefit of the present disclosure, can readily determine by simple tests suitable quantities of a particular dialkyl phenol sulfide for a particular polyethylene to give the protection desired. While the invention is especially directed to protecting polyethylene from undesirable effects of thermal processing, the dialkyl phenol sulfides also have value in protecting polyethylene against long term oxidative degradation and where such protection is desired larger quantities of dialkyl phenol sulfide can be used. It is also permissable to incorporate standard antioxidants of various types to give long term protection to polyethylene against sunlight, atmospheric an, ozone, etc.

There are numerous methods that can be used to treat ethylene polymers with sulfides of dialkyl phenols to obtain the benefits of the invention. One of the simplest is to incorporate the sulfide of dialkyl phenol during cold miliing of the polyethylene, i.e., during the treatment of polyethylene on conventional rubber mills without the deliberate addition of heat. In order to obtain maximum dispersion of the dialkyl phenol sulfide in the ethylene polymer it is preferred that the dialkyl phenol sulfide be dissolved in suitable solvent, e.g., methanol, ethanol, benzene, toluene, and that the resulting solution be added to the ethylene polymer on the rolls. Ordinarily a volatile solvent is used which will readily evaporate, although if it is permissible or desirable to incorporate a higher molecular weight solvent for the purpose of plasticizing or otherwise affecting the ethylene polymer this may be done. The dialkyl phenol sulfide can also be incorporated in the polyethylene in other mixing devices, for example, Banbury mixers, extruders. The polyethylene can be dissolved in a solvent, for example, hot aromatic hydrocarbons such as ben- Zene or xylene, the dialkyl phenol disulfide in proper amount admixed with the polyethylene solution, and

.ene subjected to .these influences.

respectively.

the solution then used for casting films, spinning fibers and similar operations that are well-known to the art, wherein the solvent is evaporated away from the polymer, resulting .in the formation of films, fibers, monofilaments and the like. It will be understood that in any of these methods of treating the polyethylene with dialkyl phenol sulfide, during such treating or before or after, conventional fillers, dyes, pigments, other polymers, and ,the like can be admixed with the polyethylene.

The flow characteristics of ethylene polymers are very important in commercial handling of same. Polyethyl- -ene is extruded into sheets, films, fibers and filaments. In these operations the rate of flow of the molten or semi-molten polyethylene greatly affects the productivity of the machine. As indicated hereinabove, processing of polyethylene at elevated temperatures in the presence of oxygen results in severe oxidative cross-linking which promptly reduces the rate of flow. Additionally, the elastic memory of the polymer is greatly increased by such oxidative cross-linking. Elastic memory can be qualitatively described as the property of a polymer to return to its original shape and size after it has under- ..gonechange in shape ,or size in molten or semi-molten conditions. Thus, as polyethylene is extruded from a die, the extruded strand tends to increase in diameter. The higher the elastic memory, the greater the increase in diameter of the strand over the diameter of the die. The same general effect is found when the polyethylene is extruded in sheets, calendered, etc. The practice of the present invention greatly minimizes or completely eliminates these adverse effects on the flow characteristics and elastic memory of polyethylene subjected to thermal treatment in the presence of oxygen. This is accomplished without undesirable side effects on the tensile strength and other properties of the polyethylene.

Furthermore, because of the very small concentrations ,needed to accomplish the stabilization, electrical properties such .as power factor and resistivity, which are very-sensitive to the presence of any polar materials, are ,not adverselyaffected. The electrical properties of polyethylene are also adversely affected byhot milling .and similar operations, and also by theaction of weather over long periods of time. The dialkyl phenol sulfides maintain ;the desirable electrical properties of polyethylsulfides are useful in very small quantities with consequent advantages in economy and the elimination of the undesirable effects produced by the addition of comparatively large quantities of stabilizer. They give no notice able color formation in the polyethylene.

In addition to the advantages already cited, the dialkyl phenol sulfides have a lubricating effect andtherefore improve the flow properties ofthe polymer in proportion to the quantity used. .This is obviously advantageous up to the point where other properties begin to be adversely affected in the processing of polyethylene.

The present invention is further illustrated, but not tobe unduly limited,.by the following examples:

EXAMPLE 1 The dialkyl phenol Tests .were made by incorporating into polyethylene .varyingconcentrations of the dialkyl phenol sulfide, or other material to be tested for comparative purposes. .Different portions of each -of the resulting polyethylene samples were then hot-milled for 15, 30 and 45 minutes, Melt index extrusion rate, and elastic memory percentage recovery, were measured on the thus- ..treatedmaterialsand also.on.the same materials not sub- Tests were made as follows. Melt index value:

(A) Extrusion rate, grams/10 minutes (B) Elastic memory, percent A steel cylindrical chamber is maintained at 190 C. A drilled orificeof 0.063 inch diameter and about 0.6 inch length is screwed into the bottom of the cylinder. A steel ram carrying a weight on the topis used to develop the extrusion pressure on the polymer. The sample to be tested is first mill-rolled for five minutes at the melting point of about *1'20 'C. and then diced in order to give a uniform product. After loading the diced particles into the extrusion chamber and placing the ram thereon, five minutes are allowed for thepolyer toreach temperature equilibrium with the chamber. The .weightis then applied to the ram and extrusionbegins. The extruding strand is cut at theorifice and a ;timer started, and the strand then cuta number of times. The cut strands are weighed and the extrusion rate reported as gramsper ten minutes. The elastic memory determination involves the measurement, by a micrometer, of the diameter of the extruded strand atthe end whichisextruded first. The percentage recovery or memory is calculated as follows:

Percentage recovery:

measured diameterorifice diameter orifice diameter Table .1

HOT WORKING STABILITY OF .POLXETHYLENE CON- 'IAINING VARYING CONCENTRATIONS OF DI-(l gglg fltglisiY-3-ME'IHYL-6-TERT-BUIYLPHENYL) MONO- Melt Index 1 .Percent Recovery Com-2 TimeofMilling, .Timeof. Milling,

2.2 1.4 0.2 0.3 07 110 .1.60 100 2.3 1.0 0.8 70 WI 120 25p.p.m 2.4 2.3 1.9 (a) 02 ,64 1 50 .m 2.5 2.4 2.6 2.5 60 ,00 01 05 100p.p.m.(0.01%) 2.4 2.4 2.4 2.4 05 07 e2 04 0.03% 2.4 2.5 2.5 2.5 74 00 03 ,69

1 Melt index extrusion rate units are gram per 10 minutes. All samplesmilled 5 minutes cold to incorporate di-(lhydroxy-3-methyl-6-t-butylphenyl) (added dissolved in 5 ml. methanol).

Milled 5 minutes cold but contained no added material. M illed 5 minutes cold and contained 5 mL'methanOl. Line through body of table separates acceptable properties (below and left of line) from unacceptable properties (above and right of line).

monosulfide TAININ GVARYIN G CONCENTRATIONS OF BUIYLATED HYD ROXY ANISOLE Melt Index 1 Percent Recovery Time of Hot Milling, Time of Hot Milling, Cone? min. min.

Melt index extrusion rate units are gram per 10 minutes.

All samples milled 5 minutes cold to incorporate the butylated hydroxy anisole.

Milled 5 minutes cold but contained no added material.

Line through body of table separates acceptable properties (below and left of line) from unacceptable properties (above and right of line).

Table III HOT WORKING STABILITY OF POLYETHYLENE CON- TAINING VARYING CONCENTRATIONS OF DIPHENYL- AMINE Melt Index 1 Percent Recovery Cone- Time of Milling, Time of Milling,

0.50% 2.4 1.9 0.3 67 so 0.70% 2.4 2.2 1.1 00 84 100 1.0% 2.5 2.2 1.1 07 70 170 2.0% 2 s 2.2 1.6 0.4 09 79 100 5.0% 6.2 2.4 1.9 )1.4 00 70 saw 100 1 Melt index extrusion rate units are grams per 10 minutes.

.411 samples milled 5 minutes cold to incorporate the d1- phenylainine.

6 Milled 5 minutes cold but contained no added mater1al.

4 Line through body of table separates acceptable properties (below and left of line) from unacceptable properties (above and right of line).

It will be seen that just 10 parts per million (0.001%) of the di-(l-hydroxy-3-rnethyl-6-tert-butylphenyl) monosulride completely protected the polyethylene against 15 minutes of hot milling, that 25 ppm. (0.00259 0) protected against 30 minutes hot milling, and that 50 ppm.

butylated hydroxy anisolc was required, while 10 times this quantity, i.e., 0.30%, was needed to protect against 30 minutes hot milling. With diphenylamine, not even 5.0%

protected the polyethylene for a 45 minute period of hot EXAMPLE 2 Electrical properties of four diilerent commercial-grade polyethylcnes, including that employed in Example 1, were determined, before and after incorporating (by 5 minutes cold milling) 50 parts per million di-(l-hydroxy- 3-mcthyl-G-tert-butylphenyl) monosulfide. The test method was that of Hartshorn and Ward, lour. Inst. Elect. EngL, November 1936, pp. 597-609. A Marconi Dielectric Test Set was used, giving the electrical dissipation factor at 1 megacyclc frequency. The dissipation factor is a measure of the amount of electrical energy converted to heat energy in tl e polyethylene under the particular conditions of test in which an alternating current is imposed on a sample of the polyethylene. The lower the dissipation factor the better the polyethylene for insulat- The data show that addition of the polar dialkyl phenol sulfide did not adversely affect the dissipation factor of the polyethylenes.

While the invention has been described herein with particular reference to various preferred embodiments thereof, and examples have been given for suitable materials, proportions and conditions, it will be appreciated that variations from the details given herein can be effected without departing from the invention.

We claim:

1. A normally solid ethylene polymer containing a small amount, up to about 0.5 weight percent but sufiicient to minimize adverse effects of thermal processing in the presence or" free oxygen, of a sulfide of a dialkyl phenol having a total of not more than 13 carbon atoms in the two alkyl groups of each dialkyl phenol residue.

2. Product of claim 1 wherein said sulfide is a monosulfide.

3. Product of claim 1 wherein said sulfide is a disulfide.

4. Product of claim 1 wherein said polymer is a homopolymer of ethylene.

5. A normally solid ethylene polymer containing as the sole antioxidant a small amount, up to about 0.5 weight percent but suificient to minimize adverse effects of thermal processing in the presence of free oxygen, of a sulfide of a monohydric dialkyl phenol in which a carbon atom of each of two nuclei of the phenol are joined together by less than three sulfur atoms and the alkyl groups contain less than six carbon atoms and at least one alkyl group is a branched chain alkyl group and which is unsubstituted, except for sulfur, in two of the positions orthoand parato the hydroxy group.

6. A normally solid ethylene polymer containing a small amount, up to about 0.5 weight percent but sufficient to minimize adverse effects of thermal processing in the presence of free oxygen, of a sulfide of an alkyl cresol having up to 12 carbon atoms in said alkyl group.

7. Product of claim 6 wherein said sulfide of an alkyl cresol has the structure:

HO Sn OH wherein R is an alkyl radical containing up to 12 carbon atoms and n is an integer less than three.

8. Product of claim 7 wherein R is a branched chain alkyl radical containing less than 6 carbon atoms.

9. Polyethylene containing as the sole antioxidant an amount, not in excess of 0.1 weight percent but suflicient to minimize adverse effects of thermal processing in the presence of free oxygen on the flow and elastic memory properties of said polyethylene, of a sulfide of a monohydric dialkyl phenol in which a carbon atom of each of two nuclei of the phenol are joined together by less than three sulfur atoms and the alkyl groups contain less than six carbon atoms and at least one alkyl group is a branched chain alkyl group and which is unsubstituted, except for sulfur, in two of the positions orthoand para to the hydroxy group.

10. Polyethylene containing as the sole antioxidant a small amount, up to about 0.5 weight percent but sufiicient to minimize adverse effects of thermal processing in the presence of free oxygen, of di(1 hydroxy 3- methyl 6 tert butyl phenyl) monosulfide.

11. Polyethylene containing as the sole antioxidant a small amount, up to about 0.5 weight percent but sufii cient to minimize adverse effects of thermal processing in the presence of free oxygen, of a sulfide of an alkyl cresol having the structure:

HO Sn OH I I R R wherein R is a branched chain alkyl radical containing less than six carbon atoms and n is an integer less than three.

12. Polyethylene containing as the sole antioxidant a small amount, up to about 0.5 weight percent but sulficient to minimize adverse ellects of thermal processing in the presence of free oxygen, of di(1 hydroxy 3- methyl 6 tert amyl phenyl) monosulfide.

13. Polyethylene containing as the sole antioxidant a small amount, up to about 0.5 weight percent but sufii- 10 cient to minimize adverse effects of thermal processing in the presence of free oxygen, of di(1 hydroxy 2- methyl-S-tert-butyl phenyl) monosulfide.

14. A composition of matter consisting essentially of polyethylene and as the sole antioxidant a small amount, up to about 0.5 weight percent but sufficient to minimize adverse effects of thermal processing in the presence of free oxygen, of a sulfide of a dialkyl phenol having a total of not more than 13 carbon atoms in the two alkyl groups of each dialkyl phenol residue.

15. A method of treating polyethylene which comprises subjecting sarne to mechanical working at elevated temperatures in the presence of free oxygen, and treating said polyethylene prior to completion of said working with, as the sole antioxidant, a small but protective amount up to about 0.5 weight percent of a sulfide of a monohydric dialkyl phenol in which a carbon atom of each of two nuclei of the phenol are joined together by less than three sulfur atoms and the alkyl groups contain less than six carbon atoms and at least one alkyl group is a branched chain alkyl group and which is unsubstituted, except for sulfur, in two of the positions orthoand parato the hydroxy group.

16. A normally solid ethylene polymer containing as the sole antioxidant a small amount, up to about 0.5 weight percent but sufiicient to minimize adverse effects of thermal processing in the presence of free oxygen, of 4,4 thiobis(3 methyl 6 tert butylphenol).

17. Polyethylene containing as the sole antioxidant a small amount, up to about 0.5 weight percent but sutficient to minimize adverse effects of thermal processing in the presence of free oxygen, of 4,4-thiobis(3-methyl-6- tert-butylphenol) 18. A normally solid ethylene polymer containing as the sole antioxidant a small amount, up to about 0.5 weight percent but sufiicient to minimize adverse eifects or" thermal processing in the presence of free oxygen, of a sulfide of a dialkyl phenol having a total of not more than 13 carbon atoms in the two alkyl groups of each dialkyl phenol residue and the sulfur bridge being para to the hydroxyl groups.

19. Stabilized polyethylene composition comprising a normally solid polymer of ethylene and between 0.05% to 0.5% by weight of the polymer of 4,4'-thiobis-(6-tertbutyl-meta cresol).

20. Stabilized polyethylene composition comprising a normally solid polymer of ethylene and a stabilizing amount below 0.5 percent of 4,4'-thiobis(6-tert-butylmeta-cresol) References Cited by the Examiner UNITED STATES PATENTS 2,434,662 1/48 Latham et a1. 260-4595 2,628,212 2/53 Young 260-4595 2,670,382 2/54 Downey 260-4595 2,675,366 8/54 Pullman 260-4595 2,716,096 8/55 Young et al 260-45'.95 2,364,338 12/64 Beaver 26045.95

LEON I. BERCOVITZ, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,170,893 February 23, 1965 Samuel Steingiser et al.

It is hereby certified that error appears I in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 69, for "electrcal" read electrical column 3, lines 63 to 69, the right-hand benzene ring should appear as shown below instead of as in the patent:

column 4, line 49, for "permissable" read permissible column 6, line 14, for "polyer" read polymer column 8, line 12, for "remarkazle" read remarkable column 9, lines 45 to 51, theright-hand benzene ring should appear as shown below instead of as in the patent:

column 10., line 57, for "8/54" read 4/54 line 59, strike out "2,364,338 12/64 Beaver 26045.95", and insert 2,364,338 12/44 Beaver -260c-45.9 5. in line 53, same column 10.

Signed and sealed this 13th day of July 1965..

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A NORMALLY SOLID ETHYLENE POLYMER CONTAINING A SMALL AMOUNT, UP TO ABOUT 0.5 WEIGHT PERCENT BUT SUFFICIENT TO MINIMIZE ADVERSE EFFECTS OF THERMAL PROCESSING IN THE PRESENCE OF FREE OXYGEN, OF A SULFIDE OF A DIALKYL PHENOL HAVING A TOTAL OF NOT MORE THAN 13 CARBON ATOMS IN THE TWO ALKYL GROUPS OF EACH DIALKYL PHEHOL RESIDUE. 